Methodology

The formula

Everything on this site comes from two lines of arithmetic on figures manufacturers publish themselves.

Wh = (mAh ÷ 1000) × nominal volts
hours = Wh ÷ watts drawn

The first line converts a battery’s capacity into energy. The second converts energy into time. Both inputs to the first are usually published. The second input to the second is almost never published, which is the gap this site exists to work around.

A worked example, start to finish

Take the pack most heated jackets ship with: 5,200 mAh at 7.4 volts, published by ororo in its own battery guide.

1. Energy. (5,200 ÷ 1000) × 7.4 = 38.5 Wh.
2. Delivery ceiling. The same guide publishes an output current of 2.5 A. 7.4 V × 2.5 A = 18.5 W. The garment cannot draw more than the pack will give.
3. Shortest possible runtime. 38.5 Wh ÷ 18.5 W = 2 hours 05 minutes. That is the floor under every claim about this pack.
4. The draw the advertising assumes. ororo publishes 8–10 hours on low. 38.5 ÷ 9 = 4.3 W. That is what the headline number describes.

Four figures, none of them ours, all of them checkable. That is the whole method, and the calculator will run it on any pack you put in.

Where each input comes from

Our source hierarchy, in order of preference:

1. Manufacturer specification sheets, battery guides and product manuals. Primary for capacity, voltage, output current, zone count and materials. Linked on every product card.
2. Live retailer data. Primary for price and availability. Never remembered, never hardcoded — see the price section below.
3. Regulatory and standards bodies. The FAA for battery transport, the EIA for electricity rates, published electrical conventions for voltage labeling.
4. Named third-party publishers, for measurements we cannot make. Always attributed in the sentence and always linked. Their measurement, credited to them.

What we never use: our own memory, another affiliate site’s unsourced claim, or a figure generated rather than found.

What we do when a spec is missing

We say so. On the page, in the table, in the cell where the number would have gone. “Not published by the manufacturer” and “not derivable” appear all over this site, and they are doing real work.

We never estimate a missing wattage. We never borrow a figure from a similar model. We never round a plausible-looking number into existence to complete a table. A blank cell that says why it is blank is more useful than a filled one you cannot trust, and it costs us nothing to be honest about it.

How we handle prices

Prices render only from a live data feed. When the feed has no current price for a product, the button reads “Check price on Amazon” and no number appears anywhere. There is no fallback to a remembered figure, because a stale price is both a disservice to you and a breach of Amazon’s own operating agreement.

Where a live price is shown, the date it was verified is shown with it. If that date is more than 48 hours old the price disappears on its own rather than waiting for us to notice.

How picks are ranked

Our rankings are an editorial judgment over published specifications, price and coverage. They are not a test result and we do not present them as one. The criteria for each roundup are written out on that roundup, so you can see what we weighted and disagree with it if you want to.

We do not publish a score out of ten. A numeric score implies a measurement process we do not have, and it would compress a judgment into a number that looks more precise than it is.

How we use other people’s measurements

Where another publisher has measured something we cannot, we cite them by name in the sentence and link the source. “Outdoor Life measured 2.5 hours on high” is a sentence we will write. “We measured 2.5 hours on high” is not, and never will be.

What this arithmetic cannot tell you

Every figure on this site is a ceiling. Real runtime lands below it, for three reasons that all push the same way:

• Cold reduces usable capacity. A lithium pack in freezing conditions delivers less than its rating — unfortunate, given what the pack is for.
• Age reduces capacity. Every charge cycle takes a little, permanently. A pack two winters old holds meaningfully less than its label.
• Conditions increase demand. The controller holds a target temperature rather than a fixed draw, so wind and movement make it run the element harder.

The manufacturer Dr. Warm, writing about its own products, describes runtime claims as a roof rather than a promise, and puts the lab-to-field swing and the wind-chill impact in the tens of percent. We think that is honest and we have adopted the same framing.

What we have not done, stated plainly

We have not worn any of this gear. We do not own it. There is no test lab, no controlled drain test, no field testing and no expert panel. Nobody here holds a credential relevant to heated apparel, and we do not claim one.

What we do have is real analytical work: reading the manuals, compiling the specifications, running the arithmetic and tracking the prices. That labor is genuinely ours and we will stand behind it. The wearing is not, and we will not claim it.

We think a reproducible calculation is a stronger thing to offer than an unverifiable claim of hands-on testing — precisely because you can check it, and prove us wrong if we are.

When we get something wrong

We fix it, and we note the correction and its date on the page. If the error changed a recommendation we say what changed and why. Silent patching is not something we do. The editorial policy sets out the process, and you can tell us if you spot something.

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